1. FIELD OF THE INVENTION
This invention relates to ethylene terephthalate polyester compositions which exhibit excellent moldability and physical properties. Particularly, the invention relates to ethylene terephthalate polyester compositions having high melt viscosity and excellent moldability, and further relates to reinforced ethylene terephthalate polyester compositions having excellent moldability, heat resistance, mechanical properties and appearance in the shaped articles obtained therefrom.
2. DESCRIPTION OF THE PRIOR ART
Polyethylene terephthalate has not been so broadly utilized in the field of molding, notwithstanding the excellent physical and mechanical properties thereof. The reason for this is mainly due to the inferior moldability of polyethylene terephthalate. Particularly, where polyethylene terephthalate of a comparatively low molecular weight is employed, it is difficult to successfully carry out molding by utilizing a usual molding machine because of the extremely low melt viscosity of the polyethylene terephthalate. For overcoming this drawback, attempts have been made to obtain polyethylene terephthalate with a high molecular weight. However, such attempts have not yet produced satisfactory results because of the inconvenient and expensive operation required to carry out the condensation-polymerization process.
Polyethylene terephthalate has a further drawback in that the shaped articles produced by using the conventional molding methods, have inferior physical properties. This is because the low rate of crystallization in the polyethylene terephthalate produces a low degree of crystallinity in the shaped articles. In order to eliminate this drawback, methods have been proposed for producing reinforced polyethylene terephthalate by adding an inorganic filler such as glass fiber to improve the rigidity of the product, or by adding a nucleator or molding through a die at a high temperature to heighten the crystallinity. However, the heat resistance of the reinforced polyethylene terephthalate obtained by using these methods is highly dependent on the crystallinity of the products, i.e. on the die temperature during the molding. Due to this factor, the resultant shaped articles are often inferior in appearance. Accordingly, these methods are not satisfactory from an economical standpoint with regard to the quality of the resultant products.